Patent GB-1062773-A (GB)
Title: Device responsive to magnetic bodies and magnetic fields
IPC: G01D5/20
Filed: 1963-11-11
Abstract: 1,062,773. Detecting magnetic bodies. HASLER A.G. Nov. 11, 1963 [Nov. 16, 1962], No. 44403/63. Heading G1N. A device responsive to stationary or moving magnetic bodies or fields includes a magnetic circuit 2 having legs 27, 28 which saturate when. pulsating current is supplied to an exciter coil 22, and having a detector coil 24 magnetically uncoupled from the exciter coil, the magnetic circuit extending between points of equal magnetic potential between the pole shoes 11, 12 of a magnet 1. Pole shoes 25, 26 are provided for magnetic circuit 2. A magnetic shunt 13 is adjustable for zero-setting, corresponding to equal leakage fluxes between pole shoes 12 and 26, and between shoes 26 and 11. If a magnetic body or field moves or lies adjacent air gap 32 pole shoe 26 becomes magnetically south with respect to pole shoe 25 and a flux is generated perpendicular to coil 24. Since the reluctance of core 2 is varied periodically on saturation by exciter coil 22, the flux passing through coil 24 varies periodically and an output is produced. Using the circuit shown in Fig. 2 magnetic bodies may be counted. AND-gates D1, D2, R3 and D3, D4, R4 produce an output only when both their inputs are negative. It is shown Fig. 3 (not shown) that a body at air gap 32 causes an output to be produced at point d while a body at 31 generates an output at e. These outputs trigger a toggle circuit to state O and state L respectively. Indicator 5 registers at every second change of state of the toggle circuit. If indicator 5 is a frequency meter it will register the rate of rotation of a gear wheel 4, which may be in a vehicle, so that the vehicle speed is measured. If the indicator is a counter it measures the distance travelled by the vehicle. As shown in Fig. 2 pulses are supplied to exciter coil 22 by connecting it in a blocking oscillator circuit, which also includes a coil 23, wound with coil 22 on branch 21 of core 2. Alternatively a single coil may be fed from a square pulse generator Fig. 4 (not shown), the coil being shunted by a diode arranged to block pulses from the generator. When each square pulse terminates current continues to flow in the exciter coil and the diode, dying away exponentially. This leads to the generation of voltages at terminals a and b of the pick-up coil, when a body is adjacent air gap 31 or 32, which has a long duration, low amplitude portion of one polarity and a short duration, large amplitude portion of opposite polarity. The AND circuit is omitted and the toggle circuit is arranged to be triggered only by a large amplitude negative pulse. Instead of shunting the exciter coil the diode may shunt a further coil coupled to the exciter coil. The position of core 2 and pole shoes 25, 26 may be adjustable. The air gaps 31, 32 may be filled with non-magnetic material to exclude magnetic particles. Branch 21 of core 2 may be omitted and the exciter coil wound in two parts on legs 27, 28. In this case the pick-up coil 24 may either be as shown, or wound in two parts also. The portions of the coils may be either in series or in parallel. The lower surface of the device may be curved, and it may be enclosed in a non-magnetic housing having a curved lower surface. A second magnet 1 may be provided on the front surfaces of pole shoes 11, 12.